1. Field of the Invention
The present invention relates to a piezoelectric stack transducer, and more specifically, to a piezoelectric stack transducer having constant output at several specific frequencies.
2. Discussion of Related Art
FIG. 1 is a diagram illustrating a conventional piezoelectric stack transducer. Referring to FIG. 1, the conventional piezoelectric stack transducer is implemented in such a manner that a plurality of piezoelectric transducers with the same thickness, diameter and material are stacked. Such a conventional piezoelectric stack transducer outputs maximum amplitude at a specific frequency and outputs reduced amplitude at frequencies other than the specific frequency, thereby resulting in greatly degraded performance.
Related prior arts will be described in detail. A piezoelectric ceramic-polymer composite capable of improving a size in a longitudinal vibration mode of a signal layer instead of restricting the size in the longitudinal vibration mode of the signal layer by forming a piezoelectric ceramic plate in a multi-layer structure having an internal electrode is disclosed in Korean Patent Laid-open Publication No. 2008-0000010 (Title: 2-2 Piezoelectric Composite Ultrasonic Oscillator having Multi-layer Structure and Method of Manufacturing The Same).
Further, a piezoelectric transducer including a piezoelectric element and an electrode, which is implanted in a middleear and converts an electrical signal corresponding to sound to a vibration signal to transfer the vibration signal to an internal ear is disclosed in Korean Patent Laid-open Publication No. 2005-0039444 (Title: Multilayer Type Piezoelectric Transducer for Middleear Implant System).